Re: [PATCH 11/18] drm/i915: switch to default context on idle

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Mar 30, 2012 at 02:17:20PM -0700, Ben Widawsky wrote:
> On Thu, 29 Mar 2012 21:29:05 +0200
> Daniel Vetter <daniel@ffwll.ch> wrote:
> 
> > On Sun, Mar 18, 2012 at 01:39:51PM -0700, Ben Widawsky wrote:
> > > To keep things as sane as possible, switch to the default context before
> > > idling. This should help free context objects, as well as put things in
> > > a more well defined state before suspending.
> > > 
> > > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > 
> > Context are yet another thing that will nicely fragment our global gtt
> > space. You don't pin them to mappable, which is a start, but I wonder
> > whether we should integrate this into our evict_something code? Although
> > that project is more involved with the current evict code, so maybe just
> > add a fixme.
> > 
> > > ---
> > >  drivers/gpu/drm/i915/i915_gem.c |    6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > > index 0985aa5..c1aab45 100644
> > > --- a/drivers/gpu/drm/i915/i915_gem.c
> > > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > > @@ -3685,6 +3685,8 @@ int
> > >  i915_gem_idle(struct drm_device *dev)
> > >  {
> > >  	drm_i915_private_t *dev_priv = dev->dev_private;
> > > +	struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
> > > +	u32 seqno;
> > >  	int ret;
> > >  
> > >  	mutex_lock(&dev->struct_mutex);
> > > @@ -3694,6 +3696,10 @@ i915_gem_idle(struct drm_device *dev)
> > >  		return 0;
> > >  	}
> > >  
> > > +	seqno = i915_gem_next_request_seqno(ring);
> > > +	i915_switch_context(ring, NULL, DEFAULT_CONTEXT_ID, seqno, 0);
> > > +	WARN_ON(i915_wait_request(ring, seqno, false));
> > 
> > This can block and potentially return early due to a signal, i.e. you need
> > to properly handle this (like the i915_gpu_idle below).
> 
> Can you elaborate? Whether or not the context switch fails, I want to
> try to idle the GPU. So I *thought* this is doing just that.

wait_request can return error codes, you need to handle them. E.g. gpu
hang, interrupt, out of memory, whatnotelse.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48